The semiconductor integrated circuit (IC) industry has experienced rapid growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. Such scaling down has also increased the complexity of processing and manufacturing ICs and, for these advances to be realized, similar developments in IC processing and manufacturing are needed. For example, the need to perform higher resolution lithography processes grows. One of the leading next-generation lithography techniques is an extreme ultraviolet (EUV) lithography. Others include X-Ray lithography, ion beam projection lithography, and electron-beam projection lithography.
EUV lithography employs scanners using light in the EUV region, having a wavelength of about 10-15 nm. Some EUV scanners provide 4× reduction projection printing, similar to some optical scanners, except that the scanners use reflective rather than refractive optics, (e.g., mirrors instead of lenses). EUV scanners provide the desired pattern on an absorption layer (“EUV” mask absorber) formed on a reflective mask. An absorption layer however may not fully absorb the incident radiation and a portion of the incident radiation is reflected through the absorption layer. This often results in an inadequate aerial image contrast, which may lead to poor pattern profiles and poor resolution, particularly as pattern features continue to decrease in size. It is desired to have improvements in this area.